MS-QA_06-2019 rev5

ANSI/AARST MS-QA 2019 34 Radon Measurement Systems Quality Assurance Laboratories—Alpha Track the processes other than the actual exposure) shall be thoroughly characterized, limited, documented and monitored by the analysis laboratory. 10.2.3 ATD Laboratory—Shelf Life Note—Shelf life varies for different device types. Because of the accrual of background, the effects of aging and possible changes to alpha sensitivity, the ATD laboratory should determine and publish, including in instructions to consumers, the time period after which the laboratory can no longer warrant the detector to be reliable. 10.3 ATD Laboratory—Calibration Relationship Note—The plastic material’s sensitivity to alpha particles, the material/analysis system’s background and aging effects on the plastic are critical parameters for this method. Although the principle of this method is based on the number of tracks in the plastic being proportional to the time-integrated radon concentration to which the plastic was exposed, the phenomenon of overlapping tracks makes the calibration relationship nonlinear for higher exposures. 10.3.1 Batch-specific Calibration Factors To maintain performance within the requirements for lower limits of detection, imprecision, total error and proportionality of ANSI/AARST MS-PC , batch -specific calibration factors are necessary. Each batch calibration must assess the effect of at least three factors (sensitivity, background and aging) on track density over the range of integrated concentrations to which the calibration relationships apply, including the nonlinear relationships for overlapping tracks. The assessment includes characterizing the sample frequency distribution (means and sample standard deviations at a minimum) that are taken from the batch regarding: — sensitivity of the plastic to alpha particles from a range of directions and within the appropriate energy range, — background track density of the plastic as processed, and — effect of aging (fading) on the plastic in terms of both sensitivity and background. Calibration characterizations are made by exposing sets of devices in a STAR and are to be conducted when there is a change in the supply of track-sensitive material, device configuration, handling and etching procedures, etchant or counting systems, or as part of an investigation due to failing QC results. It is the manufacturer’s responsibility to track QC results from different configurations and batches to monitor factors that apply to different batches of alpha-sensitive material. Note—Assessing the effects of aging on background track density and sensitivity should be conducted at least annually to generate factors that can compensate for background increases in older plastic. 10.4 ATD Laboratory—Establishment of In-Control Operations This standard presents the following principles that shall be incorporated into the laboratory’s QAP while allowing for flexibility in implementation and the derivation of limits that are specific to each laboratory and analysis system. Conducted in accordance with Section 7.7 , ATD analysis laboratories are to use limits from at least 20 independent determinations of different laboratory QC checks to monitor system performance. Although terminology and sampling procedures to meet these requirements may vary (e.g., counting tracks in 20 areas and counting tracks in 20 separate samples can both be used to characterize the distribution of track counts), basic requirements include the characterization (mean and sample standard deviation at minimum) and continued monitoring and documentation of processes and materials used during analyses and handling procedures.